1. Field of the Invention
The present invention relates to a MR/inductive type combination read/write thin film magnetic head to be mounted on the hard disk device, especially to a thin film magnetic head improved in both of the core function and shield function, and its manufacturing method.
2. Description of the Related Art
FIG. 10 is an enlarged cross section of the conventional thin film magnetic head viewed from the confronting side of the recording medium.
This thin film magnetic head belongs to a so called MR (magnetoresistance)/inductive type combination thin film magnetic head in which a reading head h1 making use of a magnetoresistance effect and a writing inductive head h2 are layered on the trailing side end face of a slider constituting a floating type magnetic head.
The reading head h1 is composed of a bottom gap layer 2 made of a non-magnetic material such as Al.sub.2 O.sub.3 (aluminum oxide) formed on a bottom shield layer 1 made of Sendust or a Ni--Fe alloy (permalloy), on which a magnetoresistive element layer 3 is formed. The magnetoresistive element layer 3 is composed of three layers of a soft magnetic layer (Soft Adjacent Layer: SAL), a non-magnetic layer (SHUNT layer) and a magnetoresistive layer (MR layer) from the bottom to the top. The magnetoresistive element layer and the non-magnetic layer are usually composed of a layer of a Ni--Fe alloy (permalloy) and a Ta (tantalum) layer, respectively, while the soft magnetic layer is formed of a Ni--Fe--Nb alloy.
Hard bias layers 4 are formed on both sides of the magnetoresistive element layer 3 as longitudinal bias layers. A main electrode layer 5 made of a material having a small electric resistance such as Cu (copper) and W (tungsten) is formed on the hard bias layers 4, a top gap layer 6 made of a non-magnetic material such as alumina being additionally formed thereon.
A bottom core layer 20 is formed on the top gap layer 6 by plating with, for example, permalloy. This bottom core layer 20 serves as a leading side core part at the inductive head h2 where the bottom core layer 20 imparts recording magnetic field to the recording medium while serving as a top shield layer at the reading head h1. The gap width G11 is determined by the gap between the bottom shield layer 1 and bottom core layer 20.
A gap layer (a layer of a non-magnetic material) 9 formed of alumina (aluminum oxide) and an insulation layer (not shown) made of polyimide or a resist material are layered on the bottom core layer 20, and a coil layer 10 patterned to form a spiral shape is provided on the insulation layer. The coil layer 10 is formed of a non-magnetic conductive material having a small electric resistance such as Cu (copper). The coil layer 10 is also surrounded by an insulation layer (not shown) made of polyimide or a resist material, a top core layer 11 formed of a magnetic material such as permalloy being plated on the insulation layer. The top core layer 11 serves as a trailing side core part of the inductive head h2 for imparting recording magnetic field to the recording medium.
The top core layer 11 is faced on the bottom core layer 20 at the confronting side of the recording medium via the gap layer 9 as shown in the drawing, forming a magnetic gap of the magnetic gap length G12 that imparts recording magnetic field to the recording medium. A protective layer 12 made of, for example, alumina is provided on the top core layer 11.
Recording electric current flows through the coil layer 10 at the inductive head h2 to impart recording magnetic field from the coil layer 10 to the top core layer 11 and bottom core layer 20. Magnetic signals are recorded on the recording medium such as a hard disk with leakage magnetic filed between the bottom core layer 20 and top core layer 11 at the magnetic gap part.
Since the bottom core layer 20 serves not only as a reading side core of the inductive head h2 but also as a top shield layer of the reading head h2 in the thin film magnetic head shown in FIG. 10 as described above, the bottom core layer 20 is required to have both properties of as a core and as a shield.
TABLE 1 below indicates magnetic characteristics required for the core function and shield function, and magnetic characteristics of the Ni--Fe alloy (permalloy) conventionally used as the bottom core layer 20.
TABLE 1 High Bs Low Hc High Hk High .mu. High .rho. Low .lambda. Low .sigma. Core function .circleincircle. .DELTA. .smallcircle. .DELTA. .circleincircle. .DELTA. .smallcircle. Shield function .DELTA. .smallcircle. .DELTA. .circleincircle. .smallcircle. .circleincircle. .smallcircle. Ni--Fe alloy 1.0 &lt;0.5 3-4 2000 18 -5 .times. 10.sup.-7 &lt;100 (T) (Oe) (Oe) (.mu..OMEGA. .multidot. cm) (MPa)
In TABLE 1, the mark .circleincircle. denotes an especially required magnetic characteristic, the mark .smallcircle. denotes a magnetic characteristic required next to .circleincircle. and the mark A denotes a magnetic characteristic that may have an appropriate value.
It is evident that a high saturation magnetic flux density (Bs) is first of all required in order to improve the core function of the bottom core layer 20 as shown in TABLE 1. While the track width should be narrowed responding to high recording density, a problem of write fringing will occur to deteriorate the recording characteristic when the saturation magnetic flux density is low.
The resistivity (.rho.) should be also made high because eddy current loss is increased at high frequency bands when the resistivity is low along with causing a problem of phase retardation (non-linear transition shift: NLTS) of the recording magnetic field due to the eddy current loss.
Anisotropic magnetic field (Hk) should be as high as possible in order to properly align magnetization along the track width direction by annealing in the magnetic field, thereby making the direction of the external magnetic field from the recording medium to be a hard axis of magnetization. A favorable magnetic inversion during recording can be attained by allowing magnetization to be properly aligned along the track width direction.
Stress (.sigma.) should be low to a certain extent for improving adhesive property.
A high magnetic permeability (.mu.) is first of all required for improving the shield function of the bottom core layer 20. Higher magnetic permeability enables excess signals (noises) from the recording medium to be absorbed by the bottom core layer 20, making it possible to properly operate the MR layer.
Magnetostriction constant (.lambda.) should be also low. The magnetic domain structure of the bottom core layer 20 is stabilized along with enabling to enhance the magnetic permeability (.mu.) by lowering the magnetostriction constant.
It is preferable that resistivity (.rho.) is high in order to suppress eddy current at high frequency bands from generating. It is also preferable that stress (.sigma.) and coercive force (Hc) are substantially low.
The saturation magnetic flux density (Bs) is not required to be so high for improving the shield function of the bottom core layer 20 as will be evident from TABLE 1, because the signal level from the recording medium is so small that magnetic saturation by the signals from the recording medium is hardly attained even when the saturation magnetic flux density is relatively small.
Although the anisotropic magnetic field (Hk) is not required to be so high, a level of at least 1 Oe (oersted) or more is necessary. When the anisotropic magnetic field (Hk) is less than 1 Oe, the magnetic field is considered to be substantially isotropic, so that magnetization can not be aligned along the track width direction even when the core is annealed in the magnetic field.
When the anisotropic magnetic field (Hk) is too high, on the other hand, the magnetic permeability (.mu.) is decreased thereby deteriorating the shield function because there is a relation as shown below between the magnetic permeability (.mu.) and anisotropic magnetic field (Hk):
.mu.=saturation magnetic flux density (Bs)/anisotropic magnetic field (Hk) PA1 b=(0.5 to 0.8).times.(100-a) and PA1 c=100-a-b in both of the upper side bottom core layer and lower side bottom core layer. PA1 forming a first bottom core layer by depositing a soft magnetic film principally containing Co and mainly composed of an amorphous structure on the insulation layer; PA1 forming a second bottom core layer by depositing a soft magnetic film containing a higher concentration of Co than the concentration of Co in the first bottom core layer and mainly composed of an amorphous structure on the first bottom core layer; and PA1 applying an annealing treatment to the first and second bottom core layers in a magnetic field at a temperature range of 200.degree. C. to 400.degree. C.
An eddy current is generated in the bottom core layer 20 at a high recording frequency to increase heat loss due to the eddy current when the bottom core layer 20 is formed of the Ni--Fe alloy, because resistivity (.rho.) of the Ni--Fe alloy is suppressed very low as shown in TABLE 1.
While the anisotropic magnetic field (Hk) of the Ni--Fe alloy is 3 to 4 Oe (oersted) as shown in TABLE 1, a higher anisotropic magnetic field (Hk) is required for the core function of the bottom core layer 20. Although the core function would be improved provided that the anisotropic magnetic field (Hk) is high, the shield function will be rather deteriorated due to decrease of the magnetic permeability (.mu.) ascribed to a high anisotropic magnetic field (Hk).
As hitherto described, it is difficult for the structure of the bottom core layer 20 to simultaneously improve both of the core function and shield function of the bottom core layer 20 that is essentially required to have different magnetic characteristics. There are also a problem of low resistivity (.rho.) in the Ni--Fe alloy as described above, making it difficult to comply with the requirement of high recording density owing to, for example, increment of heat loss by the eddy current at a high frequency band.